Many electronic devices require multiple power supplies. For example, a device with both analog and digital circuits may require +5 volts for the digital logic, and +12 Volts, -12 volts for the analog circuitry. In battery powered devices, switching power supplies are a way to create these power supplies.
A switching power supply may function by having a controller switch a transistor at high frequency. This frequency is typically in the 20 kHz to 1 MHz range. This draws current from the input power source to produce a chopped intermediate voltage that is then filtered by an L-C (inductor-capacitor) circuit to produce a smoother output voltage. The output voltage is controlled by varying the on time to off-time ratio of the transistor. Unfortunately, if there are multiple regulators in the system, the switching transistors of these multiple regulators may switch on and off in phase. This switching in phase can causes multiple regulators to be drawing current at the same time, this increases the current drain on the input power source. In fact, with enough switching transistors switching in phase, the current drain on the input power source may increase to the point where regulation cannot be maintained. Due to the high series resistance of many types of batteries, battery powered devices are particularly susceptible to this condition.
Accordingly, there is a need in the art for a multiple voltage switching power supply controller that helps lower the peak current drain on the input power source.